Nicole Gaskin, age 13, of Kingston, Ontario, Canada, for her question:

WHAT MAKES AN ECHO?

In Greek mythology, Echo was a nymph who kept up an incessant talk with Hera in order to distract her attention from her faithless husband. Discovering the trick, Hera punished Echo by taking away her power of speech until she was first spoken to, at which time she was compelled to answer. She fell in love with Narcissus, who didn't love her, and so she pined away until there wasn't anything left except her voice.  From the chatty little girls named Echo in Greek mythology comes the word we know as the reflection, or bounce back of a sound against some object.

When we give a yell or make a loud clapping sound with¬our hands, the sound waves travel in every direction. We can hear the clap or yell when the sound reaches our ears. Often the sound waves may travel to a large, distant object where they will bounce back to reach our ears a second time. This second sound, the reflected noise, is called an echo.

There can be times when we do not hear echoes, even tough reflected sound waves may be reaching our ears. We will not hear an echo, for example, if the original sound was too weak. We won't hear it either if the reflecting object is too small.

In addition, we may not hear the echo if the reflected sound hits an object less than 30 feet away. Both the original sound and the bounce back will, then reach our ears at about the same time.

Other times we may hear more than one echo from a single original sound. Repeating echoes often occur in canyons or valleys where many surfaces can reflect the sound. When this happens, sound waves will bounce from one wall to another and as a result you will hear a number of repeating echoes.

When we give a yell or make a loud clapping sound with¬our hands, the sound waves travel in every direction. We can hear the clap or yell when the sound reaches our ears. Often the sound waves may travel to a large, distant object where they will bounce back to reach our ears a second time. This second sound, the reflected noise, is called an echo.

There can be times when we do not hear echoes, even tough reflected sound waves may be reaching our ears. We will not hear an echo, for example, if the original sound was too weak. We won't hear it either if the reflecting object is too small.

In addition, we may not hear the echo if the reflected sound hits an object less than 30 feet away. Both the original sound and the bounce back will, then reach our ears at about the same time.

Other times we may hear more than one echo from a single original sound. Repeating echoes often occur in canyons or valleys where many surfaces can reflect the sound. When this happens, sound waves will bounce from one wall to another and as a result you will hear a number of repeating echoes.\

When we give a yell or make a loud clapping sound with¬our hands, the sound waves travel in every direction. We can hear the clap or yell when the sound reaches our ears. Often the sound waves may travel to a large, distant object where they will bounce back to reach our ears a second time. This second sound, the reflected noise, is called an echo.

There can be times when we do not hear echoes, even tough reflected sound waves may be reaching our ears. We will not hear an echo, for example, if the original sound was too weak. We won't hear it either if the reflecting object is too small.

In addition, we may not hear the echo if the reflected sound hits an object less than 30 feet away. Both the original sound and the bounce back will, then reach our ears at about the same time.

Other times we may hear more than one echo from a single original sound. Repeating echoes often occur in canyons or valleys where many surfaces can reflect the sound. When this happens, sound waves will bounce from one wall to another and as a result you will hear a number of repeating echoes.

You.can use an echo to tell how far away you are from an. echo producing object. Sound waves travel about one mile in five seconds, so if it takes 10 seconds for a sound to return as an echo, you know you are one mile from the object. If you're standing on one side of a canyon and your yell comes back as an echo in five seconds, you can figure the canyon is about a half mile wide.  

Did you know that echoes can also travel through water? A sounding system called sonar is used with underwater echoes to measure water depths and even to locate lost objects. Sonar is also used in the navigation of ships through narrow channels and is successfully used to locate schools of fish swimming in the ocean.